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Muscle Contraction and Metabolism in Anatomy & Physiology

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  • What is a motor unit?
    A motor unit consists of a single motor neuron and all the muscle fibers it controls.
  • What is the neuromuscular junction (NMJ)?
    The neuromuscular junction is the synapse between a motor neuron and a muscle fiber.
  • How do small and large motor units differ?
    Small motor units control few fibers for fine, precise movements, while large motor units control many fibers for powerful, gross movements.
  • Give an example of muscles with small and large motor units.
    Muscles controlling eye movements have small motor units; leg muscles have large motor units.
  • What is the primary energy source for muscle contraction?
    ATP is the primary energy source required for cross-bridge cycling, calcium reuptake, and ion gradient restoration.
  • How long does stored ATP last in muscle contraction?
    Stored ATP is depleted within 4–6 seconds during muscle contraction.
  • Name the three main pathways for ATP regeneration in muscle fibers.
    Direct phosphorylation, anaerobic glycolysis, and aerobic respiration.
  • Describe direct phosphorylation in ATP synthesis.
    Creatine phosphate donates a phosphate to ADP to form ATP, catalyzed by creatine kinase, providing energy for about 15 seconds.
  • What happens during anaerobic glycolysis in muscle metabolism?
    Glucose is broken down to produce ATP and pyruvic acid; without oxygen, pyruvic acid converts to lactic acid, which diffuses into the bloodstream.
  • What characterizes aerobic respiration in muscle ATP production?
    Aerobic respiration uses oxygen to metabolize glucose, fatty acids, and amino acids in mitochondria, producing most ATP during rest and prolonged exercise.
  • Which ATP regeneration pathway is fastest and oxygen-independent?
    Direct phosphorylation is the fastest and does not require oxygen.
  • Which ATP pathway produces lactic acid?
    Anaerobic glycolysis produces lactic acid as a byproduct.
  • Which ATP pathway provides sustained energy during prolonged exercise?
    Aerobic respiration provides sustained ATP production during prolonged exercise.
  • What energy pathways are used during short-duration, high-intensity exercise?
    Stored ATP, creatine phosphate, then anaerobic glycolysis are used.
  • What energy pathway predominates during marathon running?
    Aerobic respiration predominates during prolonged endurance activities like marathon running.
  • Name the three main types of skeletal muscle fibers.
    Slow oxidative, fast oxidative, and fast glycolytic fibers.
  • What are the characteristics of slow oxidative fibers?
    They contract slowly, use aerobic metabolism, are fatigue-resistant, and suited for endurance activities.
  • What are fast oxidative fibers best suited for?
    Medium-intensity activities like sprinting and walking; they use aerobic and some anaerobic metabolism.
  • Describe fast glycolytic fibers.
    They contract fast, use anaerobic glycolysis, fatigue quickly, and are suited for short-term, intense movements.
  • Which muscle fiber type has the highest myoglobin content?
    Slow oxidative fibers have high myoglobin content, giving them a red color.
  • What is the recruitment order of muscle fiber types?
    Slow oxidative fibers are recruited first, fast oxidative second, and fast glycolytic third.
  • Which muscle fiber type has the largest diameter?
    Fast oxidative fibers have the largest diameter.
  • How does fatigue resistance vary among muscle fiber types?
    Slow oxidative fibers have high fatigue resistance; fast oxidative have intermediate; fast glycolytic have low fatigue resistance.
  • What determines an individual's distribution of muscle fiber types?
    Genetics largely determines the distribution of muscle fiber types.